[sdiy] Negative-going triggers in the Boss DR-110 drum machine - Why?

Tom Wiltshire tom at electricdruid.net
Fri Sep 29 16:45:49 CEST 2023

> On 29 Sep 2023, at 14:57, mskala at northcoastsynthesis.com wrote:
> On Fri, 29 Sep 2023, Tom Wiltshire wrote:
>> You all seem to agree that it's down to the feeble output power of the
>> processors ports, which makes PNP transistors a better bet, and that
>> necessitates the negative-going pulses.
>> On a modern processor with much more powerful outputs we could
>> presumably (I'll have to check the currents) drop the PNPs too and use
>> positive triggers, saving even a few more parts.
> Beware of voltages.  In the schematic that was posted, the microcontroller
> and the circuit it's triggering are on different power supplies.  They
> only differ by a diode drop (6V versus 5.4V), but a "modern processor"
> would likely have 3.3V output and an analog circuit downstream might well
> need to be on a higher power supply voltage than that even if the
> microcontroller can source a fair bit of current at its own power voltage.
> Putting the microcontroller port into open-drain mode and using
> negative-going pulses would in many cases be the best way to interface it
> to a circuit on a higher-voltage supply.

Yes, good point!

Thanks Matthew.


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